1. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Passive gamma emission tomography (PGET) Tapani Honkamaa

2. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Contents Introduction Description of the method Motivation Project history and timeline Prototype Hardware Prototype Software Results from the test campaigns Summary and future directions

3. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Introduction Research on Passive gamma emission tomogropgy (PGET) started already in 1980’s R&D has been and is conducted specifically under R&D programmes made for the IAEA nuclear material safeguards and financed my its member states safeguards support programmes – Hungary, – Sweden – USA, – Finland – EC

4. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Description of the method rotation fuel assembly scanned section scanning direction

5. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Head1 Head2 104 detectors Housing Tungsten collimator And with more detectors arranged in 2 heads: Heads consist of detectors and multislit tungsten alloy collimator With sufficient number of detectors need for lateral movement is eliminated and only rotational movement is needed Detector spacing 4 mm, resulting in 2mm resolution.

6. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Head1 Head2 104 detectors CdTl 2x5x10mm Housing Main signal: 1274 keV Fission product Eu-154 Gamma-ray -compton edge. Tungsten collimator Geometry Requirement: imaging of Spent nuclear fuel assembly PWR type 17x17 rods in rectangular lattice Resulting to the need 2 heads, 104 detectors in each, detector spacing 4 mm, resulting in 2mm overall resolution.

7. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Data production and imaging Cross sectional image of fuel assembly Image calculation Fuel Assembly Measurement (scanning) Projections at several angles

8. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Strength of PGET Method is accurate, it is capable of detecting a single missing pin inside a fuel assembly – true partial defect method

9. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY About nuclear material safeguards

10. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Goal of Nuclear Material Safeguards – Never again Picture: Charles Levy, 9th of Aug 1945

11. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY What it takes to build a nuclear weapon? Nuclear material (U or Pu) – Difficult to get. – Main effort in nuclear non-proliferation is put in here! Other components – Rather easy to get Information and Expertise – In general, this indormation is restricted by international agreements – Adequate information is available publicly to build a primitive device

12. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY …Why verification is conducted in nuclear material safeguards? In order to prevent proliferation of nuclear weapons spent nuclear fuel in under stringent control all over the world. The control is exercised by international and national inspectorates – International Atomic Energy Agency (IAEA) European Commission and national regulators. Implementation of non-proliferation regime requires that declarations and reports provided by nuclear operators can be verified. Verification tools are needed

13. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Why Passive Gamma Emission Tomography? Current verification tools have quite limited sensitivity to so called partial defects: Partial defect = part of the fuel diverted to nondeclared purposes IAEA Policy: a partial defect test with high detection probability on all populations of easily dismountable spent fuel transitioning to storages where re-verification is either difficult or even impossible. – PGET strength is in its extraordinary sensitivity – PGET would be an important component of the tool box of complementary partial defect test devices. One interesting application: last verification before fuel assemblies are moved into a geological repository for final storage.

14. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Final disposal of spent nuclear fuel

15. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Construction project of PGET prototype

16. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Project timeline 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 Kick-off Specifications PO for arrays Hardware construction Delivery of arrays System integration Ringhals test System repair&integration Ispra tests Olkiluoto Loviisa Reporting Ringhals Ispra Ollkiluoto Loviisa

17. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Prototype, head open

18. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Software Two parts: Control Software and Data Processing Software 1.Control Software, attended – Input: set up of the detectors and detector electronics and fuel information – Output: The unprocessed (raw) data – Control software automatically invokes the data processing software. 2.Data Processing Software, automatic – Input: Raw data Corrections are applied to the raw data, diagnostic modules, etc. – Data analysis can be performed automatically Manual operation is possible for test/calibration. – Output: information whether pins are missing as compared against a set of operator declared information including fuel type – cross sectional image.

19. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Prototype schema.. ….And in real life! Notebook with ports Driver + PSU Array 1 104 detectors electronics Array 2 104 detectors electronics MOTOR with position encoder UNDERWATER HEAD AIR WATER

20. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Some technical issues in system integration Longest delay was in delivery of detectors. Procurement, 18 mo delivery time, first acceptance test failed Some problems: detector arrays do not operate reliably, the read out is working only in serial mode, and stepping motor generates disturbances to the detector signals. Serial readout is a major issue. – With present prototype measurement time is 1-3 h instead of 2-5 minutes

21. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Passive gamma emission tomographic measurements, Ringhals 16-20 Nov 2009

22. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ringhals tests Detector failure prevented the measurements Overheating of one ASIC (each head consists of 4 ASICs, each controlling 26 detectors (4x26=104) Grounding issues: Stepping motor rotating 2x150 kg arrays takes a lots of Amperes. Repair took a few months, then recalibrations, putting things together, combating against grounding problems, etc.

23. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ringhals 16-20 Nov 2009

24. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ringhals 16-20 Nov 2009

25. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ringhals 16-20 Nov 2009

26. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ringhals 16-20 Nov 2009

27. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Passive gamma emission tomographic measurements, Ispra 11-15 Jul 2012

28. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ispra 11-15 Jul, 2012

29. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ispra 11-15 Jul, 2012

30. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ispra 11-15 Jul, 2012

31. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Measured objects, results The fuel items were simple 6, 8 and 12 rod objects Long cooling time, low signal, long measuring times needed Result: Imaging was successful The data provided by another array was not satisfactory – However, resolution provided by another array was sufficient The calibration was not perfect – Did not prevent of having results The simple objects are not the real test for the usability of the method. – Self absorbtion is negligible. However, this was the first successful campaign for the prototype.

32. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

33. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

34. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY

35. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Ispra conclusions The simples objects are not the real test for the usability of the method. However, this was the first successful campaign for the prototype.

36. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Passive gamma emission tomographic measurements, Olkiluoto BWR 15-17 Mar 2013

37. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Measured objects, results The fuel items were 8x8 and 10x10 spent fuel assemblies Cooling time varied from 3 to 32 y Result: Imaging was successful, with some artifacts Again: The data provided by another array was not satisfactory – However, resolution provided by another array was sufficient The calibration was made better, but yet not at desired level – Did not prevent of having results First successful campaign for the prototype with real NPP fuel.

38. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY 8x8-1 fuel

39. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY 10x10-9 fuel

40. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Passive gamma emission tomographic measurements, Loviisa 15-17 Jan 2014

41. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Work prior the test Removing faulty detectors Recalibration Analysis software development for VVER fuel (BUTE) – Modified for hexagonal fuel

42. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Setup

43. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Fuel VVER 440 type fuel is hexagonal – Full assembly has 126 rods, center location is always empty – Challenging geometry due to high self-absorption One assembly out of 6 had missing rods 5 assemblies measured, one twice

44. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Results

45. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Assembly with 3 missing rods

46. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Low-resolution image, noise reduced

47. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Loviisa Observations Measurement of one assembly took 2-3 hours, due to complex design of the fuel 120 scans were needed (compared 48-60 for BWR) The measurement of the fuel with missing pins was repeated due to poor statictics The system was able to provide image immediately after measurement In overall the system functioned well, two problems were observed: – A few distorted profiles out of 120 was generated due to HW malfunction: this is not critical for imaging VVER 440 assembly, they were left out of analysis. – Uniformity of measureing channels was not perfect, some corrections were applied during the analysis

48. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Summary and future directions A Passive Gamma Emission Tomograph has been designed, manufactured and successfully tested under IAEA support Programme task JNT 1510. System is able to detect missing pin from BWR and VVER-440 assemblies. Successful tests with PWR fuel are not yet conducted, but simulations predict that the result is most likely successful.

49. SÄTEILYTURVAKESKUS STRÅLSÄKERHETSCENTRALEN RADIATION AND NUCLEAR SAFETY AUTHORITY Summary and future directions Readiness for deployment and availability for real verifications need to be sustained – New project established Improvement of the electronic readout is a prerequisite – Shorten the measurement times Next important steps will be to provide unattended operation More in depth understanding about analysis is needed – Quantitatively evaluate the cooling time and burnup for each fuel rod – Effect of rods with burnable poisons Work continues now more intensively – Goal is to have the functional, reliable and tested system available by 2023, when final disposal of spent nuclear fuel in Finland begins.